1. Field of the Invention
The present invention relates generally to a multilayer ceramic device used in high frequency wireless devices such as mobile telephones, and relates more particularly to a multilayer ceramic RF device.
2. Description of Related Art
Multilayer ceramic devices, and particularly multilayer ceramic radio frequency (hereinafter referred to as RF) devices operating in the RF band, have contributed greatly to size reductions in mobile telephones and other high frequency wireless devices. A typical conventional multilayer ceramic RF device is described below with reference to FIG. 12 and FIGS. 13A-E.
FIG. 12 is a section view of a conventional multilayer ceramic RF device having a low temperature sintered ceramic layer 101 and multilayer circuit conductors forming an RF circuit 102. Also shown in FIG. 12 are via holes 103 and chip components 105 such as resistors, capacitors, inductors, and other packaged semiconductor chip components. A metal cap 107 shields the various chip components 105.
The operation of this conventional multilayer ceramic RF device is described next below.
The multilayer circuit conductor 102 electrically interconnects the chip components 105, and forms intralayer capacitors and intralayer inductors inside the low temperature sintered ceramic layer 101. Collectively, these various components form an RF circuit so that the device functions as a multilayer RF switch or other multilayer ceramic RF device.
FIGS. 13A-C are a block diagram showing the configuration of a conventional multilayer ceramic RF device. These individual discrete devices function as a multilayer filter (FIG. 13A), a surface acoustic wave (hereinafter referred to as SAW) filter (FIG. 13B), and an RF switch (FIG. 13C).
It will be noted that the construction described above does not have a sealing resin protecting the surface mounted chip components, or a metal sealant cap (metal cap 107) sealing a cavity. The resulting problem is that bare semiconductor devices, SAW filters, and other components that must be sealed cannot be incorporated in the RF device. The conventional metal cap 107 shown in FIG. 12 simply provides an electromagnetic shield and does nothing to seal the device, and the above-noted components therefore cannot be provided.
Furthermore, the above-described device has a single ceramic layer. As taught in Japanese Patent Laid-open Publication (kokai) H4-79601 (U.S. Pat. No. 5,406,235), it is possible to monolithically mold ceramic layers or other dielectric bodies having different dielectric constants as a way to incorporate a built-in high capacitance capacitor and achieve a multiple function device. Such a device can be produced by, for example, monolithically sintered ceramic layers of different compositions. The problem here is that ceramics of different compositions have different contraction and expansion coefficients, and molding by monolithic sintering is therefore very difficult. A parasitic capacitance affecting device characteristics can also form between ceramic layers of different dielectric constants in monolithically molded ceramic devices made from ceramics of different dielectric constants.
With consideration for the problems described above, it is an object of the present invention to provide a multilayer ceramic device capable of incorporating components such as bare semiconductor devices and SAW filters.
A further object of this invention is to improve device functionality, reduce device size and profile, improve manufacturability, and improve device reliability.
A yet further object of this invention is to improve overall performance of a multilayer ceramic device providing plural functions with optimized circuit design.
To achieve the above objects, a multilayer ceramic device according to the present invention has a first ceramic layer having a first multilayer circuit pattern electrically connected through interlayer via holes; a second ceramic layer having a second multilayer circuit pattern electrically connected through interlayer via holes; and a thermosetting resin sheet disposed between the first and second ceramic layers. The thermosetting resin sheet has a through hole filled with a conductive resin electrically interconnecting the first multilayer circuit pattern in the first ceramic layer with the second multilayer circuit pattern in the second ceramic layer.
The ceramic layers have at least one internal circuit pattern layer, and the circuit patterns are electrically connected through the via holes. The ceramic layers are preferably made from a high dielectric constant material with a dielectric constant of 10 or higher, and a low dielectric constant material with a dielectric constant less than 10. It is noted that the dielectric constant may be similar to relative dielectric constant.
Exemplary high dielectric constant materials include Bixe2x80x94Caxe2x80x94Nbxe2x80x94O (dielectric constant=58), Baxe2x80x94Tixe2x80x94O and Zr(Mg, Zn, Nb)xe2x80x94Tixe2x80x94Mnxe2x80x94O.
Exemplary low dielectric constant materials include alumina borosilicate glass (dielectric constant=7), and forsterite ceramics.
Exemplary thermosetting resins include epoxy resin, phenol resin, and cyanate resins.
The ceramic layers of a multilayer ceramic device according to the present invention are preferably made of a multilayer monolithic, low temperature co-fired ceramics (LTCC).
Further preferably, the first and second ceramic layers are in unity with the thermosetting resin sheet. More preferably, the first and second ceramic layers are thermoset together with the thermosetting resin to be in unity.
Yet further preferably, the first and second ceramic layers each have a different dielectric constant.
As noted above, the ceramic layers have different dielectric constants, and the dielectric constant of the thermosetting resin sheet disposed between the ceramic layers is lower than the dielectric constant of either ceramic layer. The construction of the multilayer ceramic device reduces the parasitic capacitance that occurs between ceramic layers of different dielectrics, and improves device characteristics.
Forming a pattern at the interface between the ceramic layer and thermosetting resin sheet also makes it possible to avoid loss and adjust for mismatched impedance occurring between the multilayer circuit pattern and other circuits formed inside the ceramic layers.
It should be noted that there is little interference between patterns formed at the interface to the ceramic layer, and good device characteristics can be achieved, because the dielectric constant of the thermosetting resin is extremely low.
Yet further preferably, a multilayer ceramic device according to this invention has a third ceramic layer having a third multilayer circuit pattern electrically connected through interlayer via holes; and a thermosetting resin sheet disposed between the second and third ceramic layers. The dielectric constant of the first ceramic layer is less than 10; the dielectric constant of the second ceramic layer is 10 or higher; and the dielectric constant of the third ceramic layer is less than 10.
Yet further preferably, the third ceramic layer is substantially as thick as the first ceramic layer, and the second ceramic layer is thicker than the first and third ceramic layers.
Yet further preferably, the thickness of the first ceramic layer is different from that of the second ceramic layer.
Yet further preferably, a land grid array terminal is disposed to the second ceramic layer on a side thereof not facing the other ceramic layer.
This land grid array is used for electrical connection to the circuit board when the multilayer ceramic device is mounted on a circuit board.
Yet further preferably, a thermosetting resin sheet is disposed between the second ceramic layer and the land grid array terminal.
Disposing a thermosetting resin layer between the bottom of the bottom ceramic layer of the device and the land grid array terminals disposed to the same bottom improves the drop strength of the bottom of the ceramic device. In addition, using a thermosetting resin with a dielectric constant lower than the dielectric constant of the ceramic layer reduces parasitic components with the circuit board, enables impedance matching to be changed, and provides greater freedom in circuit design.
Yet further preferably, the first ceramic layer has a semiconductor bare chip and a SAW filter of which the electrode part is sealed airtight and mounted face down on a surface of the first ceramic layer not facing the second ceramic layer. The electrode part of the bare chip and SAW filter faces the first ceramic layer surface, and the tops thereof are coated with a sealing resin.
Exemplary semiconductor bare chips include bipolar transistors, FET, diodes, and ICs, and are made from silicon and other compound semiconductor materials. The SAW filter is a single crystal piezoelectric element of quartz, lithium tantalate (LiTaO3) or lithium niobate (LiNbO3), for example. These components can be mounted face down, that is, with the electrodes electrically connected facing the surface of the ceramic layer on which the component is mounted, by using stud bump bonding (SBB), gold to gold interconnection (GGI), or other bump connection technique.
Yet further preferably, the first ceramic layer has a recess at the top thereof, and a semiconductor bare chip and a SAW filter are mounted on the cavity bottom with an electrode part thereof facing the cavity bottom, and the top thereof coated with a sealing resin.
Yet further preferably, the first ceramic layer has a hole part. A semiconductor bare chip and a SAW filter are mounted on a surface of the thermosetting resin sheet forming the bottom of the hole part, and a top of the bare chip and SAW filter are coated with a sealing resin.
In addition, the dielectric constant of the first ceramic layer is less than 10, and the dielectric constant of the second ceramic layer is 10 or more.
Yet further preferably, the semiconductor bare chips include a semiconductor bare chip that operates at a frequency in the ultra high frequency (UHF) band or higher.
Yet further preferably, the semiconductor bare chips include a PIN diode. Further preferably, the SAW filter has an unbalanced input, balanced output terminal structure.
A multilayer ceramic device according to a further aspect of the invention has a first ceramic layer having a first multilayer circuit pattern electrically connected through interlayer via holes; and a second ceramic layer having a second multilayer circuit pattern electrically connected through interlayer via holes. The second ceramic layer is layered on the first ceramic layer. The first ceramic layer has mounted on a surface thereof not facing the second ceramic layer a semiconductor bare chip and a SAW filter, the electrode part of which is sealed. The electrode part of the bare chip and SAW filter faces the first ceramic layer surface, and the tops thereof are coated with a sealing resin. The second ceramic layer has a land grid array terminal disposed to a surface of the second ceramic layer not facing the first ceramic layer.
Further preferably, the first and second ceramic layers of this multilayer ceramic device each have a different dielectric constant.
Yet further preferably, the first ceramic layer has a recess at the top thereof, and a semiconductor bare chip and a SAW filter are mounted on the cavity bottom with an electrode part thereof facing the cavity bottom, and the top thereof coated with a sealing resin.
Yet further preferably, the multilayer ceramic device also has a third ceramic layer having a third multilayer circuit pattern electrically connected through interlayer via holes. The third ceramic layer is laminated to a surface of the second ceramic layer not facing the first ceramic layer. In this multilayer ceramic device, the dielectric constant of the first ceramic layer is less than 10, the dielectric constant of the second ceramic layer is 10 or higher, and the dielectric constant of the third ceramic layer is less than 10.
A multilayer ceramic device according to a further aspect of the invention has, laminated in order, a first ceramic layer having a recess at a top part thereof and a first multilayer circuit pattern electrically connected through interlayer via holes; and a second ceramic layer having a second multilayer circuit pattern electrically connected through interlayer via holes. The first ceramic layer has a semiconductor bare chip and a SAW filter mounted on the cavity bottom with an electrode part thereof facing the cavity bottom, and the top thereof coated with a sealing resin.
Further preferably, an electrode pattern is formed on a flat surface part of the first ceramic layer on the side of the first ceramic layer not facing the second ceramic layer, and this electrode pattern forms an array antenna.
The mobile terminal device includes a display and a communication member. The communication member has a multilayer ceramic device. Further, the multilayer ceramic device has a first ceramic layer, a second ceramic layer, and a thermosetting resin sheet. The first ceramic layer has a first multilayer circuit pattern electrically connected through interlayer via holes. The second ceramic layer has a second multilayer circuit pattern electrically connected through interlayer via holes. The thermosetting resin sheet is disposed between the first and second ceramic layers. Also, the thermosetting resin sheet has a through hole filled with a conductive resin electrically interconnecting the first multilayer circuit pattern in the first ceramic layer with the second multilayer circuit pattern in the second ceramic layer.
Exemplary mobile terminal devices include mobile telephone, and the like. As mentioned above, the multilayer ceramic may be reduced device size and be improved device functionality, therefore the mobile terminal device may be reduced device size and be improved device functionality.